<template>
    <div class="pagination">
      <!-- 上 -->
      <button :disabled="pageNo == 1" @click="$emit('getPageNo', pageNo - 1)">
        上一页
      </button>
      <button
        v-if="startNumAndEndNum.start > 1"
        @click="$emit('getPageNo', 1)"
        :class="{ active: pageNo == 1 }"
      >
        1
      </button>
      <button v-if="startNumAndEndNum.start > 2">···</button>
      <!-- 中间部分 -->
      <button
        v-for="(page, index) in startNumAndEndNum.end"
        :key="index"
        v-if="page >= startNumAndEndNum.start"
        @click="$emit('getPageNo', page)"
        :class="{ active: pageNo == page }"
      >
        {{ page }}
      </button>
   
      <!-- 下 -->
      <button v-if="startNumAndEndNum.end < totalPage - 1">···</button>
      <button
        v-if="startNumAndEndNum.end < totalPage"
        @click="$emit('getPageNo', totalPage)"
        :class="{active:pageNo==totalPage}"
      >
        {{ totalPage }}
      </button>
      <button
        :disabled="pageNo == totalPage"
        @click="$emit('getPageNo', pageNo + 1)"
      >
        下一页
      </button>
   
      <button style="margin-left: 30px">共 {{ total }} 条</button>
    </div>
  </template>
   
  <script>
  export default {
    name: "Pagination",
    props: ["pageNo", "pageSize", "total", "continues"],
    computed: {
      //总共多少页
      totalPage() {
        //向上取证
        return Math.ceil(this.total / this.pageSize);
      },
      //计算出连续的页码的起始数字与结束数字[连续页码的数字:至少是5]
      startNumAndEndNum() {
        const { continues, pageNo, totalPage } = this;
        //先定义两个变量存储起始数字与结束数字
        let start = 0,
          end = 0;
        //连续页码数字5【就是至少五页】，如果出现不正常的现象【就是不够五页】
        //不正常现象【总页数没有连续页码多】
        if (continues > totalPage) {
          start = 1;
          end = totalPage;
        } else {
          //正常现象【连续页码5，但是你的总页数一定是大于5的】
          //起始数字
          start = pageNo - parseInt(continues / 2);
          //结束数字
          end = pageNo + parseInt(continues / 2);
          //把出现不正常的现象【start数字出现0|负数】纠正
          if (start < 1) {
            start = 1;
            end = continues;
          }
          //把出现不正常的现象[end数字大于总页码]纠正
          if (end > totalPage) {
            end = totalPage;
            start = totalPage - continues + 1;
          }
        }
        return { start, end };
      },
    },
  };
  </script>